The objective of this study is to analyze the heterogeneity of the prereplicative portion of the cell cycle with the purpose of determining whether entry into, and emergence from the quiescent state, as well as cell cycle traverse can be explained in terms of a cellular clock. In addition, the work will compare cells at the extremes of the proliferative state with respect to their ability to precisely order cellular events and to make the transition from the resting proliferative state.